Method and means for operating a steam gas plant including a gas turbine, a steam turbine with its steam generator at the downstream end

ABSTRACT

Method and means for operating a steam gas plant including a gas turbine, and a steam turbine with its steam generator at the downstream end. The method and means for improving the operation of a steam gas plant comprising a gas turbine the exhaust gases of which sustain the combustion of the burners of a steam generator, which latter feeds steam into a steam turbine. A fraction of the exhaust gases is diverted through an adjusting damper into the steam generator at a point where the temperature of the flue gases approximates that of said exhaust gases. Said point may lie beyond a reheater inserted for instance between two stages of the steam turbine and ahead of a heat exchanger.

United States Patent Vidal etal.

45] July 11, 1972 [54] METHOD AND MEANS FOR OPERATING A STEAM GAS PLANT INCLUDING A GAS TURBINE, A STEAM TURBINE WITH ITS STEAM GENERATOR AT THE DOWNSTREAM END |72| Inventors: Jean Vidal, Ville DAvray; Jean Parbot; Jacques Lemolne. both of Paris. all of France [73] Assignee: Stein Industrle, Paris. France [22] Filed: May 13, 1970 [2i] Appl.No.: 36,762

[52] US. Cl... ..60/39.l8 B [51 1 Int. Cl. ..F02c 7/02, F02g 5/02 [58] FleldofSeanrh ..60/39.l8,39.l8A, 39.188,

60/39.l8 C, 39.!8 R

[56] References Cited UNITED STATES PATENTS 2.663.145 12/1953 Waeseiynck ..60/39.l8 B

3,304,7l2 2/1967 Pacault et ........,......60/39.l8 B 3,325,992 6/l967 Sheldon ..60/39.i8 B 3,374,621 3/!968 Pacault et al ..60/39. I 8 B Primary Examiner-Martin P. Schwadron Assistant Examiner-Allen M. Ostrager A|rome \Amo|d Robinson l l ABSTRACT Method and means for operating a steam gas plant including a gas turbine, and a steam turbine with its steam generator at the downstream end.

The method and means for improving the operation of a steam gas plant comprising a gas turbine the exhaust gases of which sustain the combustion of the burners of a steam generator, which latter feeds steam into a steam turbine A fraction of the exhaust gases is diverted through an adjusting damper into the steam generator at a point where the temperature of the flue gases approximates that of said exhaust gases. Said point may lie beyond a reheater inserted for instance between two stages of the steam turbine and ahead of a heat exchanger.

SCIainmlDrawingflgure METHOD AND MEANS FOR OPERATING A STEAM GAS PLANT INCLUDING A GAS TURBINE, A STEAM TURBINE WITI'I ITS STEAM GENERATOR AT THE DOWNSTREAM END Our invention relates to a steam gas plant including a gas turbine, a steam turbine with its steam generator at the downstream end, wherein the output of the gas turbine is connected with the burners of a downstream steam generator, associated with heat exchangers adapted to transmit the heat produced by the steam generator to the steam feeding the steam turbine.

Our invention has more specifically for its object a method for operating a plant of this type showing in particular the advantage of providing means for adjusting the temperature of the superheated steam without any expenditure of auxiliary energy and without any reduction in the total efficiency of the cycle.

According to our invention, only a fraction of the exhaust gases produced by the gas turbine is sent into the burners of the steam generator and the remainder of said exhaust gases is sent into the output of the steam generator at a point where the temperature of the flue gases approximates that of the exhaust gases.

Our invention has also for its object a plant of the abovementioned type intended for the execution of such an improved method. Said plant is characterized by the fact that the gas turbine is additionally connected with the output of the steam generator.

We have described hereinafter by way of example and in a non-restrictive manner an embodiment of our improved plant, reference being made to the single FIGURE of the accompanying drawing illustrating said plant diagrammatically.

As illustrated the plant according to our invention includes, in a conventional manner a compressor 1 fed at 2 with atmospheric air and feeding a combustion chamber 3 provided with a burner 4. The chamber 3 is connected with a gas turbine 5 the shaft of which drives the compressor 1 together with an auxiliary alternator 6.

The output of the turbine 5 is connected with the burners of a steam generator 7 which burners are thus fed by the gases issuing from the turbine 5 and containing still large amounts of oxygen. Said burners are also connected with an input of fuel 8, the fuel being injected into the steam generator so as to burn in the gas fed by the turbine and serving a combustion sustaining medium. The steam generator 7 contains a superheater 9, a reheater It and three economizers or heat exchangers 10, 12a and 12b, the flue gases flowing in contact with these different parts before they are exhausted and flow out through the chimney 13.

The plant comprises also a turbine including two stages or groups of stages 14a and 14b. The input of the stage or group of stages [40 is connected with the output of the superheater 9 while its output is connected with the input of the reheater II. The input of the second stage or group of stages 14b is connected with the output of the reheater ll while its output is connected with the input of a pump 15 through the agency of a condenser 16. The output of the pump 15 is connected with the input of the superheater 9 through the agency of a series of heating means l7 to which heat is applied in a conventional manner by steam tapped off the turbine 14a, 14b. The economizers 12a and 12b are inserted in parallel with a number of said heating means and are connected with the input of the superheater 9 through the economizer l0. Lastly a main alternator I8 is driven by the shaft of the turbine 14a, 14b.

For the different loads of the plant, the highest efficiency is reached when constancy is obtained for the temperature of the reheated steam admitted into the stage 14b of the steam turbine.

Hitherto, this temperature of the reheated steam was adjusted either by recycling a fraction of the flue gases passing out of the steam generator 7, which leads to a certain consumption of auxiliary energy or else by injecting water into the input of the reheater 11, which leads to a reduced efficiency for the steam turbine 14a, 141;.

According to the invention, it is possible to adjust the tem' perature of the reheated steam while cutting out said drawbacks by connecting additionally the output of the turbine 5, through a pipe 19 in which is inserted an adjusting damper 20, with the output of the steam generator at a point on the downstream side of the reheater ll. Said pipe l9 opens into the steam generator 7 at a point where the temperature of the flue gases approximates the temperature of the exhaust gases passing out of the turbine 5.

Since the gas turbine 5 operates independently of the steam generator 7, the amount of exhaust gases does not follow the demand of said steam generator and operation of the damper 20 provides means for adjusting, in conformity with the demand of the steam generator, the throughput of gas fed into the burners of said generator together with the throughput of gas fed to a point on the downstream side of the reheater l 1.

Consequently, the throughput of flue gases passing through the reheater 11 and that of the gases sent into the burners of the steam generator are both governed by the position assumed by the damper 20.

Since the heat is transmitted to the reheater II by the flue gases passing out of the steam generator 7 mainly through convection, the steam temperature depends on the throughput of flue gases passing through the steam generator and therefore on the position assumed by the damper 20.

On the other hand, the injection of a fraction of the exhaust gases passing out of the gas turbine into a point on the downstream side of the reheater ll produces an increase in the minimum entropy since the temperature of the flue gases passing out of the steam generator approximates at such a point the temperature of the exhaust gases.

The amount ofexhaust gases injected into the burners of the steam generator 7 remains always large enough for the combustion of the fuel injected into them and, provides under all conditions of operation a suitable excess of air.

The method according to the invention shows in particular the following advantages:

it leads to an improvement in the general efficiency of the steam gas plant since it allows the oxygen carried by the exhaust gases of the gas turbine 5 to serve for the combustion of the fuel injected into the steam generator 7.

it allows the execution of a simultaneous adjustment of the temperature of the reheated steam and of the amount of combustion-sustaining gases feeding the burners of the steam generator 7 by resorting to extremely simple apparatus it produces an increased minimum entropy of the system since it is possible according to said method to send into the steam generator 7 a fraction in the exhaust gases produced by the gas turbine 5 at a point of the steam generator where the temperature of the flue gases approximates that of said exhaust gases.

Obviously, our invention should not be considered as limited to the embodiment described and illustrated and it covers in contradistinction all the modifications thereof falling within the scope of the accompanying claims. Thus it is possible to provide heat recovering means different from those illustrated and to execute through operation of the damper 20 adjustments different from those disclosed hereinabove.

What we claim is:

1. In a method for operating a steam gas plant comprising a gas turbine, a steam generator, burners fed by the exhaust gases of said gas turbine for heating said generator, at least one heat exchanger in said generator and a steam turbine fed by said steam generator, the step comprising dividing said exhaust gases of said gas turbine into two fractions and feeding said fractions respectively into said burners and into the output of said steam generator at a point ahead of one said heat exchanger where the temperature of the flue gases of said generator approximates that of said exhaust gases.

2. A method as claimed in claim 1 adapted for operating a steam gas plant including a reheater and heat exchangers incorporated with the steam generator, wherein the fraction of exhaust gases fed into the output of the steam generator reaches the latter at a point beyond the reheater and ahead of at least one heat exchanger.

3. A method as claimed in claim 1 according to which the ratio between the two fractions is controlled.

4. ln a steam gas plant consisting of a gas turbine, a steam generator, burners within said steam generator connected to the exhaust of said gas turbine, a steam turbine connected to said steam generator, heat exchangers and a superheater incorporated within said steam generator, the improvement comprising means for diverting a fraction of the exhaust gases 

1. In a method for operating a steam gas plant comprising a gas turbine, a steam generator, burners fed by the exhaust gases of said gas turbine for heating said generator, at least one heat exchanger in said generator and a steam turbine fed by said steam generator, the step comprising dividing said exhaust gases of said gas turbine into two fractions and feeding said fractions respectively into said burners and into the output of said steam generator at a point ahead of one said heat exchanger where the temperature of the flue gases of said generator approximates that of said exhaust gases.
 2. A method as claimed in claim 1 adapted for operating a steam gas plant including a reheater and heat exchangers incorporated with the steam generator, wherein the fraction of exhaust gases fed into the output of the steam generator reaches the latter at a point beyond the reheater and ahead of at least one heat exchanger.
 3. A method as claimed in claim 1 according to which the ratio between the two fractions is controlled.
 4. In a steam gas plant consisting of a gas turbine, a steam generator, burners within said steam generator connected to the exhaust of said gas turbine, a steam turbine connected to said steam generator, heat exchangers and a superheater incorporated within said steam generator, the improvement comprising means for diverting a fraction of the exhaust gases from the exhaust of said gas turbine and remixing same in the output end of said steam generator after said super-heater and ahead of at least one heat exchanger.
 5. A steam gas plant as claimed in claim 4 comprising further a reheater for the steam carried inside the steam generator , said reheater located at a point ahead of the point at which said fraction of the exhaust gases is diverted.
 6. A steam gas plant as claimed in claim 4 comprising a damper adapted to adjust the throughput of the diverted fraction of exhaust gases. 